Electrical connector question

ok so ill try and word this best as i can im just wondering on the 4pin connector with the starter cable on it is the gas gauge wire in it aswell? the connector im talking about is on the passenger side at the bottom of the firewall leading onto the frame rail.
right now in my truck my gauge isnt working plus before midnight shift my truck wouldnt start it has power because i can listen to my system and my compressors and you can hear no power loss(even had it hooked up with cables to another car)
i didnt really get time to troubleshoot the problem just noticed in my clutter of unplugged connectors(have a weber installed) i notice another 4pin one around the same location but im off to bed now hopefully thats all the problem is

gas guage wire comes out the harness on the back passenger side of the cab & runs to the gas tank....the sending unit is prolly corroded & needs cleaning or replacing.

the harness that runs to the starter has just that , the starter wire, and a wire for the ptc heater that went under the carb, one for the oil pressure sender on the side of the block, and one or two more, can't remember right off the top of my head, none of which should keep the truck from starting unless there is a prob with the starter wire, or if you still have the main fuse block on the wheel well, one of those may be blown...

ok so i located the problem i guess when i was hooking up all my wires (comps & amps) to my new battery terminals i pulled a piggy back wire that was in the connector i thought was unplugged now my current question is how exactly would i piggy back this back the correct way or why it was piggy backed in the first place? any info would be awesome

^^ DUDE costa i luv ur truck .. something about it ... IDK

......anybody got any help for me...?
and thanks man really appreciate it its a 3yr project of mine..that paint alone is what sets my truck as a love it or hate it project..some ppl like it some ppl dont but w/e your trucks coming along too